1. Field of the Invention
The present invention relates to a semiconductor structure and manufacturing methods thereof, and in particular, to a semiconductor structure with inward curving spacers and manufacturing methods thereof.
2. Description of the Prior Art
As semiconductor processes advance to the very deep sub micron level, how to increase the driving current for MOS transistors has become a critical issue in this field.
To attain higher performance of a semiconductor device, attempts have been made to use a strained silicon (Si) layer for increasing the mobility of electrons or holes. Taking advantage of a stressor is a common way to increase the effect of the MOS transistors. Forming a tensile or a compressive stressor on the substrate and using the MOS transistors to change the band structure of silicon can increase mobility of electrons.